History of animals ~700 million years old
- Chemical evidence in sediments of fossils that is found in modern sponges
- Accepted fossils from Ediacaran (pre-Cambrian)
- mollusks, cnidarians and sponges
- Animals diversify across Paleozoic, Mesozoic and Cenozoic
- punctuated by mass extinctions

Animals are monophyletic
- All animals, excepts sponges, have:
- Nerve cells called neurons
- Muscle cells
- Animals are incredibly diverse
- 35 major phyla
- 1/3 are marine
- most phyla have marine members




Invertebrates: lacking a backbone
- 95% of known animal species
- Occupy every habitat on Earth
- Groupings characterized by tissue layers,symmetry and unique structures

Phylum Porifera (Sponges)
- Most basal animal group
- marine
- adults do not move
- filter feeders
- hermaphroditic (alternate)
- Lots of cells, but
no tissue layers
- Share similarities with protist Chonaflagellates
- feed using cells called
choanocytes


Phylum Cnidarian
- Animals except sponges are considered “True Animals”

Phylum Cnidarian
- Animals except sponges are considered “True Animals”
- First lineage to diversify were Cnidarians
- corals, hydras and jellyfish
- pre-Cambrian
- Simple
diploblastic radial body plan
- motile and sessile
- polyp or medusa forms

Basic Cnidarian body plan (
Nematocyst on phylogeny)


Most animals are triploblastic, bilaterians

-
Triploblasty = 3 germ layers
-
Bilateral = symmetrical in 2 halves
Most animals are triploblastic, bilaterians

-
Triploblasty = 3 germ layers
-
Bilateral = symmetrical in 2 halves
- 3 major clades of bilaterians
- Lophotrochozoa
- Ecdysozoa
- Deuterostomia
Lophotrochozoa: Most share 2 structures
-
Lophophore: crown of ciliated tentacles for feeding
-
Trophophore: distinctive larval stage
- beating cilia
- cylinder body

Lophotrochozoa - 18 total phyla
- Platyhelminthes (flatworms)
- Syndermata (rotifers)
- Brachiopods (lamp shells)
- Mollusca (snails, slugs, oysters, clams, octopuses, squids)
- Annelids (segmented worms)
- Many phyla appeared in Cambrian explosion


Phylum Platyhelminthes (flatworms)


Phylum Mollusca: Snails, slugs, clams, mussels, octopus & squid


Phylum Annelida: Earthworms (
segmentation on phylogeny)


Ecdysozoans
- Animals with cuticle
- shed tough external coat
- shed as grow;
molting; ecdysis
- 8 total phyla
- more species than all other groups
- Nematoda (roundworms)
- Arthropods (mostly insects)

Phylum Nematoda (round worms)
- Cylinder bodies from 1mm to 1m
- Aquatic, soil, plant tissues, animals tissues
- many parasitic species
- humans are host to 50 species
- Longitudinal muscles; thrashing motion

C. elegans: model animal species


Phylum Arthropoda: Rulers of the animal world
- A billion billion arthropods estimated
- 1 million species described
- nearly all habitats on Earth
-
Segmented body, hard exoskeleton, jointed appendages
- Early arthropods (Trilobites) had little variation in body plan
- Evolution selected for functional body regions

Arthropod body plans: unique Hox genes

Phylum Echinoderms: Next time

